Summary This Supplement is focused on an expansion of Aim 3 of the parent grant, wherein we proposed to analyze the misregulated erythroid phenotype seen in cells derived from a congenital dyserythropoietic (CDA) type IV patient. These rare patients contain a mutation in EKLF/KLF1 at E325K. Although availability of a derived induced pluripotent stem (iPS) cell line provided a firm basis for this Aim, its inherent limitations remained. These will be overcome by the three goals described in this Supplement. These entail incorporation of novel genetic methods, cellular expansion protocols, and the availability of patient samples, all via collaborations not envisioned in the original parent grant. These dramatically expand the scope of the original proposal and directly address the limitations of the original Aim 3.